The isolation and structure elucidation of compounds from the Hawaiian marine algae Laurencia nidifica and Dictyota acutiloba is being performed. The crude extracts from these algae have shown considerable antibiotic activity. Seventeen compounds have been isolated from the L. nidifica, four of which appear to be responsible for the biological activity. Eleven of these compounds have structures not previously reported in the literature. Two compounds with novel structures have been isolated from the D. acutiloba.